1. Field of the Invention
The present invention relates to an electric junction box. More specifically, the present invention relates to an electric junction box to be installed in an automobile and includes a power distributor. The power distributor includes a heat sink attached to a circuit construct. The circuit construct includes relays, as well as other electronic components, mounted on one side of a circuit board and bus bars fixed on the other side of the circuit board.
2. Description of Related Art
Conventionally, an electric junction box, such as a junction box for distributing electric power to each of the wire harnesses in an automobile, has a large number of relays and fuses, and a large number of connector-connecting portions formed on the outer surface of the box for connecting bus bar circuits to wire harnesses. The bus bar circuits are contained inside the electric junction box. In recent years, the number of electrical circuits in an automobile has increased in accordance with the sharp increase in the number of electronic components installed in an automobile, particularly as the automobile has become more sophisticated. Therefore, the number of relays mounted in an electric junction box for installation in an automobile has become larger, which in turn has forced the electric junction box to become more dense, as well as larger.
In response thereto, an electric junction box has been provided having a power distributor (PD) built therein. The PD includes semiconductor switching devices (FET) and mounting relays such as SMD relays mounted on a printed circuit board, and a heat sink fixed on the other side of the printed circuit board.
For example, in Japanese Laid Open Patent Publication No. 2001-319708, shown in FIG. 10 of the present application, electric junction box 1 is disclosed, which includes power distributor PD 2 and branch circuit block 5. In PD 2, semiconductor switching device (FET) 3 is mounted on a printed circuit board; a bus bar is fixed on the back-side of the printed circuit board; FET 3, which requires large electrical current, is connected to the bus bar; and heat sink 4 is attached to the bus bar. Branch circuit block 5 is made from the lamination of bus bars and insulation plates. On the lower surface of case 6 of electric junction box 1, connector housings 7 are provided for permitting insertion of connectors of wire harnesses (not shown in the figure) installed in a vehicle. On the upper surface of case 6, fuse housing 8 is provided. Connector housing 7 and fuse housing 8 are connected to branch circuit block 5.
However, as it stands now, PD 2 of electric junction box 1 is designed as an exclusive part for each specific vehicle family by using a single circuit board. When making a design for a new vehicle family or when a design change is required, the design and manufacturing process of PD 2 has to be started anew, thereby causing an additional burden in the design process, as well as increasing production and management costs. In recent years, since space efficiency for installing electric junction box 1 in a vehicle has been a primary concern, a distance between electronic components mounted on PD 2 has become narrower, thereby making it difficult to respond promptly when a design change is required. In particular, the design load has become extremely large when making PD designs for vehicle families with large differences in specifications, and vehicle families with different types of engines, such as, diesel engines and gasoline engines.
In addition, in the electric junction box 1 shown in FIG. 10, since PD 2 is laterally juxtaposed to branch circuit block 5 in a horizontal surface direction, a problem exists in that the installation space required for installing electric junction box 1 in a vehicle becomes large. When PD 2 is laminated on the lower surface of branch circuit block 5 for the purpose of minimizing the horizontal area of electric junction box 1, it puts restrictions on locations for connector housings 7. Since power input and output between a wire harness (not shown in the figure) and PD 2 are done almost completely via branch circuit block 5 from connector housings 7, when designing the arrangement of connectors for each destination, a problem arises in that circuit wirings of PD 2 and branch circuit block 5 become very complicated.
It would be advantageous to simplify the design for an electric junction box having a built-in PD. The present invention is provided to address the above-described problems.